This invention relates generally to a method and apparatus which mixes a polymeric flocculent in dilution water and activates the polymer for liquid/solid separation and more particularly to a polymer activation and dilution method and apparatus which activates a batch of dry polymer in a dilution chamber, without damaging the polymer structures excessively, to produce a polymer for particular use in the treatment of water.
Flocculent and coagulants such as polyelectrolyte materials, polymers, gums and the like ("polymers") are commonly used in water treatment equipment in order to remove solids suspended in the water. Polymers are high molecular weight materials with millions of charge sites that attract the suspended particles. However, for a polymer to perform properly, the polymer must extend or untangle in dilution water. A polymer so extended is defined as being fully activated.
As disclosed in patent application Ser. No. 07/370,375 incorporated herein by reference, optimum activation of a polymer in dilution water requires a solution of dispersed polymer and dilution water to be subjected to a high shear rate agitation for a relatively short contact time to initiate activation and dissolution of the polymer. However, as the polymer begins to dissolve in the dilution water, the polymer molecules become more susceptible to physical damage from the high shear mixing. Therefore to further the dissolution and speed the activation process, the polymer solution is then subjected to a lower energy or low shear rate mixing for a longer period of time.
Polymers may be supplied in many different forms. One of the forms, a dry polymer such as a dry synthetic polyelectrolyte for example, is very difficult to properly activate. Unless a dry polymer is almost immediately dispersed into the dilution water when the polymer first comes into contact with the water, the tangled polymer molecules tend to attract each other, resulting in the formation of large clumps or agglomerations of polymer particles. Once formed these agglomerations are difficult to activate and are ineffective in liquid solid separation.
Prior art systems which are used to activate dry polymers typically rely on a continuous two step procedure consisting of a high shear dispersion followed by low shear mixing. The high shear dispersion is generally accomplished by combining dry polymer and a small amount of dilution water either a dynamic or jet mixer to form a slurry of dispersed polymer particles in dilution water. The slurry is then transported to a separate low shear mixer typically by a pressurized conduit. In the low shear mixer, tightly controlled flow amounts of the slurry and additional dilution water are mixed to achieve the desired solution concentration.
One of the drawbacks of this type of activation system is the large amount of capital investment required for the equipment and instrumentation needed for these systems. If a small amount of activated polymer is needed, such as in the treatment of potable water, these systems are uneconomic.
Another drawback is that the static mixers rely on a constant dilution water pressure and flow rate. In many locations, the water supply system cannot provide the needed constant water pressure and flow rate.
To provide for the small volume applications, a polymeric emulsion containing dispersed polymer particles may be used. However, polymer emulsions contain a hydrocarbon oil continuous phase making up about 50% of the total volume; and therefore, can only be applied in very small doses. Also, due to the health concerns, polymer emulsions require lengthy regulatory approval. Finally polymer emulsions have a limited shelf life and in remote locations this limited shelf life undesirable.
It is therefore an object of the present invention to provide an apparatus which can economically activate a small volume of dry polymer. A related object is to provide an apparatus for small volume applications which does not require the use of a polymer emulsion.
Another object of the present invention is to provide a method and apparatus for dry polymer activation which does not rely on a constant dilution water pressure and flow rate to function properly.